A study is proposed of the biochemistry of 2'5' oligoadenylate (2-5A) and its role in the mechanism of action of interferon. The enzyme that synthesizes this unusual oligonucleotide will be purified from primary cultures of chick embryo cells treated with interferon. Antisera will be raised by injecting rabbits with the purified enzyme, and these antisera will be used to immunoprecipitate 2-5A synthetase from the products of cell-free translation of mRNA from interferon-treated cells. This will provide a quantitative assay for 2-5A synthetase mRNA, enabling the response of this interferon-inducible gene to be studied at the transcriptional level. The mRNA will be quantitated, characterized, and partially purified. The role of the 5' terminal triphosphate group in the action of 2-5A will be determined by synthesizing analogues of 2-5A that have methylene bridges between the beta and gamma phosphates. The levels of 2-5A synthetase activity will be assayed in peripheral lymphocytes taken from patients undergoing interferon therapy.